Giardia and crytosporidium contamination in surface water: from where, by how and does identification method matter?.

Abstract

Water is an important vehicle for infection by Giardia and Cryptosporidium to animal and human. Both protozoa contaminate surface water from various sources such as household sewage, runoff from animal husbandry and pet excreta. Since residents along the Chao Phraya River are known to use raw water daily for various purposes including bathing,cleaning cutlery and laundry, contamination is a highly likely threat to the residents in the area. The Department of Drainage and Sewerage of Bangkok Metropolitan is responsible for the household water drainage to Chao Phraya River. Potential contamination is most likely from sewage discharge by both the residents and factories along the river. We collected 5 sets, each of 6 water samples from the river at the drainage station at varying times, and examined for Giardia and Cryptosporidium contamination by various methods, namely 1) Sucrose floatation and Fluorescence assay (SF-FA),2) mmunomagnetic separator (IMS) and 3) Fluorescent in situ Hybridization (FISH) and 4) Real-time PCR. The possible sources of those contaminations were then identified by using the genotyping method. Giardia was tested positive between 46.8 – 63.3% with mean (min-max) concentration at 2.13 (0-7) cysts/L and Cryptosporidium between 30 – 73.3% with 1.01 (0-4.5) oocysts/L. Household sewage was identified as the source of surface-water contamination. SF-FA is a simple method but it is time consuming and need an experienced technician. IMS is widely used due to its high efficiency, rapidity and required less examiner’s experiences. Apart from cost, its recovery rate will also be decreased when used in high water turbidity, low or high water pH and high iron particle interference sample. FISH provides a convenient and cost-effective technique for visualizing micro-organisms, whilst they are structurally intact. However, application of FISH to wastewater samples generates high background fluorescence due to their organic and inorganic content which might mimic with the studied protozoa. The combination of excellent sensitivity and specificity, low contamination risk, ease of performance and speed, has made real-time PCR technology an appealing method for use in the environmental samples for diagnosing protozoa contamination. Each identification method has its own advantages and limitations. Researchers have to select the appropriate method for their particular situation.